This invention relates to antenna reflectors and more particularly to a method of measuring the accuracy of an antenna reflector surface.
It is well known in the electronics industry that accurate antenna reflector surfaces are required to form antenna beams with maximum efficiency and minimized side lobes. The ability to obtain the required accuracy becomes more difficult at higher frequencies and in particular in the microwave region on up. Antenna reflector manufacturers strive to obtain accurate reflector surfaces, but it then becomes necessary to measure the surface accuracy to evaluate their efforts and to project electrical performance. Various optical and mechanical means of measurement have been devised to obtain RMS (root-mean-square) surface errors, but in all known methods to date, a relatively elaborate, expensive and time consuming process is involved. In many of these methods, the usual procedure involves the utilization of a template having a curved edge conforming to the desired curvature of the reflector surface. Preferably the template is a full diameter template rather than a radial template. Great care is taken to mount the template over the reflector surface and both the reflector diameter plane and the template diameter plane must be very carefully levelled. This relationship must then be maintained as the template is revolved in order to measure the surface deviation from the curved edge of the template. It is, therefore, necessary to construct an accurate fixture which employs precision bearings. The measurements are then taken with feeler type gauges.
To simplify matters, attempts have been made to measure the RMS surface error by laying the template on the surface and obtain data by utilizing feeler gauges. This method is simple but it can produce errors in the RMS surface error determination of greater than 50% of the true value. A major cause of this error is the fact that the rise and fall of the template with rotation is not detected or taken into account. The surface accuracy will then appear better than it actually is.